Solid electrolyte battery and production method thereof

ABSTRACT

Disclosed is a solid electrolyte battery including: a first electrode including a first collector, and a first active material layer formed on one surface of the first collector with an outer peripheral edge portion of the first collector remaining as a collector exposed portion; a second electrode including a second collector and second active material layers formed on both surfaces of the second collector; and a solid electrolyte interposed between the first electrode and the second electrode; wherein the second electrode is held in the first electrode in such a manner that the first active material layer is opposed to each of the second active material layers via the solid electrolyte, and is sealed in the first electrode by joining the collector exposed portion of the first electrode to each other. This battery is allowed to be further thinned and reduced in weight, to be improved in energy density per weight and energy density per volume, and to be enhanced in air-tightness.

RELATED APPLICATION DATA

The present application claims priority to Japanese Application No.P2000-072513 filed Mar. 10, 2000, which application is incorporatedherein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

The present invention relates to a thin type solid electrolyte batteryand a production method thereof.

In recent years, along with the progress of the electronic technology,there have been strong demands toward higher performances,miniaturization, and portableness of electronic apparatuses. To meetsuch demands, batteries used for these electronic apparatuses have beenrequired to have high energy densities, and from this viewpoint, studieshave been actively made to develop nonaqueous electrolyte batteries. Inparticular, lithium batteries or lithium ion secondary batteries, havingexcellent performances, for example, electromotive forces higher thanthose of conventional batteries, such as 3 or 4 V, have been adopted forvarious portable electronic apparatuses such as cam coders, portabletelephones, and notebook type personal computers.

Of the above-described lithium ion secondary batteries, a solidelectrolyte battery using a solid electrolyte, having merits, forexample, a property allowed to be thinned and freely foldable, has beenactively studied. Examples of the solid electrolytes may include agel-like electrolyte composed of a solid electrolyte containing aplasticizer and a high polymer solid electrolyte composed of a highpolymer in which a lithium salt is dissolved.

To make effective use of the merits, that is, the characteristicsallowed to be thinned and reduced in weight, of these nonaqueouselectrolyte batteries, for example, Japanese Patent Laid-open No. Sho57-115820 has disclosed a nonaqueous electrolyte battery of a type inwhich a battery element is enclosed by using, as a container, aso-called laminate film formed by holding metal foil or a metal layersuch as a metal vapor-deposition layer between resin layers. In thisbattery, a heat seal layer constituting the innermost layer of thecontainer, that is, the laminate film is made from a resin such asacrylic acid denatured polyethylene or acrylic acid denaturedpolypropylene ionomer, which resin exhibits a relatively goodair-tightness at ordinary temperature. However, batteries mounted onrecent electronic apparatuses, for example, personal computers have beenrequired to exhibit a heat resistance at 85° C. In such a hightemperature environment, the above-described nonaqueous electrolytebattery may cause a problem that the resin forming the heat seal layerbe peeled from the metal layer, thereby degrading the air-tightness ofthe battery.

To solve the above problem, Japanese Patent Laid-open No. Hei 9-288996has disclosed a nonaqueous electrolyte battery of a type in which aninsulating layer made from a material excellent in a barrier performanceagainst an electrolytic solution such as polyethylene terephthalate isdisposed between a heat seal layer constituting the innermost layer anda metal layer of a container. In this battery, by heat-sealing thecontainer in which the insulating layer is provided between the heatseal layer and the metal layer, it is possible to prevent the peeling ofthe heat seal layer from the metal layer by suppressing permeation ofthe electrolytic solution between the metal layer and the heat seallayer, and hence to ensure a relatively high air-tightness even in ahigh temperature environment.

However, in the case of using the container having the above-describedheat seal layer for a thin type sheet-like solid electrolyte battery,the container becomes thick because of the presence of the heat seallayer, to thereby increase the total thickness of the solid electrolytebattery. That is to say, because of the container including the heatseal layer, it fails to make effective use of the merits of the solidelectrolyte battery, that is, the characteristics allowed to be thinnedand reduced in weight. Further, since the proportion of the constituentelements not contributing to the battery reaction to the entire batterybecomes large, there occurs an inconvenience that the energy density perweight and the energy density per volume are reduced.

The solid electrolyte battery using the container including the heatseal layer presents another problem that since the resin forming theheat seal layer is exposed from a side surface of the outer peripheraledge portion of the container, the inner side of the heat seal layer isexposed to the electrolytic solution and the outer side thereof isexposed to outside air, with a result that a trace of moisture permeatesthe interior of the battery through the exposed heat seal layer withelapsed time, thereby deteriorating the cycle characteristic of thebattery.

A further problem of the solid electrolyte battery using the containerincluding the heat seal layer is that the width of a so-called stickingmargin given to the outer peripheral edge portion of the container mustbe extended for desirably heat-sealing the container. As a result, sincethe area of the sticking margin not contributing to the battery reactionbecomes large, the energy density of the battery is degraded.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a solid electrolytebattery allowed to be further thinned and reduced in weight, to beimproved in energy density per weight and energy density per volume, andto be enhanced in air-tightness, and to provide a method of producingthe solid electrolyte battery.

To achieve the above object, according to a first aspect of the presentinvention, there is provided a solid electrolyte battery including: afirst electrode including a first collector, and a first active materiallayer formed on one surface of the first collector with an outerperipheral edge portion of the first collector remaining as a collectorexposed portion; a second electrode including a second collector andsecond active material layers formed on both surfaces of the secondcollector; and a solid electrolyte interposed between the firstelectrode and the second electrode; wherein the second electrode is heldin the first electrode in such a manner that the first active materiallayer is opposed to each of the second active material layers via thesolid electrolyte, and is sealed in the first electrode by joining thecollector exposed portion of the first electrode to each other.

With this configuration, since the first collector serves as thecontainer, it is possible to eliminate the need of provision of aterminal through which the first electrode is connected to the externaland also provision of the container. Further, since the collectorexposed portion of the first electrode is directly joined to each othernot via a resin for heat seal, it is possible to obtain a significantlydesirable air-tightness and also to significantly reduce the area of thecollector exposed portion of the first electrode functioning as thejoining margin.

To achieve the above object, according to a second aspect of the presentinvention, there is provided a method of producing a solid electrolytebattery, including the steps of: forming a first active material layeron one surface of a first collector with an outer peripheral edgeportion of the first collector remaining as a collector exposed portion,to produce a first electrode; forming second active material layers onboth surfaces of a second collector, to produce a second electrode;holding the second electrode in the first electrode in such a mannerthat the first active material layer is opposed to each of the secondactive material layers via a solid electrolyte; and joining thecollector exposed portion of the first electrode, in which the secondelectrode has been held in the holding step, to each other, to seal thesecond electrode in the first electrode.

With this configuration, since the collector exposed portion of thefirst electrode functioning as the joining margin is directly joined toeach other not via a resin for heat seal to be thus sealed, it ispossible to produce a thin, lightweight, and air-tight solid electrolytebattery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an embodiment of a solidelectrolyte battery of the present invention;

FIG. 2 is a sectional view, taken on line A-B of FIG. 1, showing thesolid electrolyte battery shown in FIG. 1;

FIG. 3 is a sectional view, taken on line C-D of FIG. 1, showing thesolid electrolyte battery shown in FIG. 1;

FIG. 4 is a perspective view showing a state in which a negativeelectrode is held between a pair of positive electrodes;

FIG. 5 is a perspective view showing a state in which the negativeelectrode is held between the pair of positive electrodes viaseparators;

FIG. 6 is a perspective view showing another embodiment of a solidelectrolyte battery of the present invention;

FIG. 7 is a sectional view, taken on line E-F of FIG. 6, showing thesolid electrolyte battery shown in FIG. 6;

FIG. 8 is a sectional view, taken on line G-H of FIG. 6, showing thesolid electrolyte battery shown in FIG. 6;

FIG. 9 is a perspective view showing further another embodiment of asolid electrolyte battery of the present invention;

FIG. 10 is a sectional view, taken on line I-J of FIG. 9, showing thesolid electrolyte battery shown in FIG. 9; and

FIG. 11 is a sectional view, taken on line K-L of FIG. 9, showing thesolid electrolyte battery shown in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment of a solid electrolyte battery ofthe present invention will be described with reference to the drawings.

FIG. 1 is a view showing an embodiment of a solid electrolyte battery inthis embodiment; FIG. 2 is a sectional view taken on line A-B in FIG. 1;and FIG. 3 is a sectional view taken on line C-D in FIG. 1. A solidelectrolyte battery 1 has a pair of positive electrodes 2 as firstelectrodes, a negative electrode 3 as a second electrode sealed in thepositive electrodes 2, a negative electrode terminal 4 physically,electrically connected to the negative electrode 3, a sealing member 5disposed between the negative electrode terminal 4 and the positiveelectrodes 2, and a pair of solid electrolyte layers 6.

The positive electrode 2 has a positive collector 2 a and a positiveactive material layer 2 b formed on one surface of the positivecollector 2 a. The positive active material layer 2 b is not formed onthe one surface of an outer peripheral edge portion of the positivecollector 2 a. Such an exposed outer peripheral edge portion is taken asa positive collector exposed portion 2 c.

The negative electrode 3 has a negative collector 3 a, and negativeactive material layers 3 b formed on both surfaces of the negativecollector 3 a. At a terminal extraction port formed at a position of theouter peripheral edge portions, butted to each other, of the positiveelectrodes 2, the negative electrode terminal 4 is covered with thesealing member 5 to be thus insulated from the positive electrodes 2,and is lead to the outside of the solid electrolyte battery 1.

As shown in FIGS. 2 and 3, the negative electrode 3 having the negativeactive material layers 3 b on both surfaces of the negative collector 3a is held between the pair of positive electrodes 2 in such a mannerthat the negative active material layers 3 b are opposed to the positiveactive material layers 2 b with the pair of solid electrolyte layers 6put therebetween, and the negative electrode 3 is sealed, together withthe pair of the solid electrolyte layers 6, in the positive electrodes 2by joining the positive collector exposed portions 2 c, which are formedat the outer peripheral edge portions of the positive electrodes 2 andwhich function as joining margins, to each other.

In the solid electrolyte battery 1 having the above configuration, thepair of the positive electrodes 2 seal the negative electrode 3 and thesolid electrolyte layers 6 therein by joining the positive collectorexposed portions 2 c to each other with the positive collectors 2 adirected outwardly. That is to say, the positive collectors 2 a functionnot only as collectors of the positive electrodes 2 but also as acontainer for sealing the interior of the solid electrolyte battery 1from outside air. Accordingly, it is possible to eliminate the need ofprovision of the container, which has been required to contain a batteryelement composed of the positive electrodes 2, the negative electrode 3and the solid electrolyte layers 6.

In particular, since it is not required to provide the container for thethin type sheet-like solid electrolyte battery 1, it is possible toreduce the thickness of the solid electrolyte battery 1, and hence tofurther thin the battery 1. As a result, it is possible to make full useof the merits, that is, the characteristics allowed to be thinned andreduced in weight, of the solid electrolyte battery 1 using a gel-likeelectrolyte or a high polymer solid electrolyte, and further, since theneed of provision of the container can be eliminated, it is possible toimprove the energy density of the battery.

In the conventional battery, since a battery element is sealed by aninsulating container, each of the positive electrode 2 and the negativeelectrode 3 must be lead to the outside via an electrode terminal;however, according to the solid electrolyte battery 1 in thisembodiment, since the positive electrodes 2 serve as the container, allof the portions of the battery 1 except for the negative electrodeterminal 4 can function as the positive electrode terminal. Accordingly,although only the negative electrode 3 sealed in the battery is requiredto be provided with a negative electrode terminal, it is possible toeliminate the provision of a new positive electrode terminal for thepositive electrode, and hence to realize further lightweightness andspace-saving of the solid electrolyte battery 1. Since an electronicapparatus on which the solid electrolyte battery 1 is mounted can bedesigned with no limitation to a position at which the positiveelectrode terminal is present, it is possible to realize thelightweightness and space-saving of the electronic apparatus.

According to this solid electrolyte battery 1, the positive collectorexposed portions 2 c provided at the outer peripheral edge portions ofthe positive electrodes 2 are used as the joining margins, and aredirectly joined to each other without use of a resin for heat seal, toseal the negative electrode 3 and the solid electrolyte layers 6.Accordingly, it is possible to prevent moisture from permeating theinterior of the solid electrolyte battery 1 via the resin for heat sealand thereby positively keep the air-tightness of the interior of thebattery, and hence to prevent the deterioration of thecharging/discharging cycle due to permeation of moisture.

Since the positive collector exposed portions 2 c provided at the outerperipheral edge portions of the positive electrodes 2 are directlyjoined to each other not via a resin for heat seal, the width of each ofthe positive collector exposed portions 2 c can be made narrower thanthat of the related art sticking margin for heat seal. As a result, itis possible to reduce the areas of the positive collector exposedportions 2 c not contributing to the battery reaction, and hence tofurther improve the energy density of the battery.

The negative collector 3 a can be formed by metal foil made from copper,nickel, or stainless steel. In the case where being sealed in the solidelectrolyte battery 1, the negative collector 3 a can be formed into notonly the shape of foil but also a shape of lath, punching metal, ornetwork. Taking into account the thinning of the solid electrolytebattery 1, the thickness of the negative collector 3 a is preferably ina range of 30 μm or less.

In the case of applying the solid electrolyte battery 1 of the presentinvention to a lithium primary battery or a lithium secondary battery,as a negative active material contained in the negative active materiallayer 3 b, there is preferably used lithium, a lithium alloy, or amaterial into or from which lithium can be doped or released. As thematerial into or from which lithium can be doped or released, there canbe used a carbon material such as a difficult-to-graphitize carbon basedmaterial or a graphite based material. Specific examples of these carbonmaterials may include pyrolytic carbons, cokes, graphites, vitreouscarbon fibers, sintered organic high polymer compounds, carbon fibers,and activated charcoals. Specific examples of the above cokes mayinclude pitch coke, needle coke, and petroleum coke. The sinteredorganic high polymer compound can be produced by sintering phenol resinor furan resin at a suitable temperature, thereby carbonizing the resin.

In addition to the above carbon material, a high polymer such aspolyacetylene or polypyrrole, or an oxide such as SnO₂ can be used asthe material into or from which lithium can be doped or released.Further, as the above-described lithium alloy, there can be used alithium-aluminum alloy.

As the positive collector 2 a, there can be used metal foil made fromaluminum, nickel, or stainless steel. In the case where being sealed inthe solid electrolyte battery 1, the positive collector 2 a can beformed into not only the shape of foil but also a shape of lath,punching metal, or network. Taking into account the thinning of thesolid electrolyte battery 1, the thickness of the positive collector 2 ais preferably in a range of 30 μm or less.

As a positive active material contained in the positive active materiallayer 2 b, a metal oxide, a metal sulfide, or a specific high polymercan be used depending on the kind of the battery used.

For example, in the case of applying the solid electrolyte battery 1 ofthe present invention to a lithium primary battery, TiS₂, MnO₂,graphite, or FeS₂ can be used as the positive active material. In thecase of applying the solid electrolyte battery of the present inventionto a lithium secondary battery, a metal sulfide such as TiS₂, MOS₂, orNbSe₂, or a metal oxide such as V₂O₅ can be used as the positive activematerial. Further, a transition metal oxide containing lithium expressedby a chemical formula LiM_(x)O₂ (M is one or more kinds of transitionmetals and x is a value depending on a charging/discharging state of thebattery and usually set in a range of 0.05 to 1.10) can be used as thepositive active material. The transition metals M contained in thetransition metal oxide containing lithium are exemplified by Co, Ni, andMn. Specific examples of the transition metal oxides containing lithiummay include LiCoO₂, LiNiO₂, LiN_(y)Co_(1−y)O₂ (O<y<1) , and LiMn₂O₄.such a transition metal oxide containing lithium becomes an excellentpositive active material because it can generate a high voltage andensure a high energy density. From the viewpoint of ensuring a largecapacity, an oxide of manganese or a composite oxide of lithium andmanganese having a spinel type crystal structure is preferably used asthe positive active material. The above-described positive activematerials may be used for the positive active material layer 2 b singlyor in combination.

The solid electrolyte layer 6 may be made from a high polymer solidelectrolyte having a diaphragm property and an adhesion property, or agel-like electrolyte formed by adding a plasticizer to the high polymersolid electrolyte.

For example, the high polymer solid electrolyte is formed by diffusingan electrolyte salt in a matrix polymer.

Specific examples of the electrolyte salts may include LiPF₆, LiClo₄,LiCF₃SO₃, LiAsF₆, LiBP₄, LiN(CF₃SO₃)₂, and C₄F₉SO₃Li. These salts can beused singly or in combination. In particular, LiPF₆ is desirable fromthe viewpoint of ion conductivity.

The chemical structure of the matrix polymer is not particularly limitedinsofar as the matrix polymer itself or the gel-like electrolyte usingthe matrix polymer exhibits an ion conductivity of 1 mS/cm or more atroom temperature. Specific examples of the matrix polymers may includepolyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, apolysiloxane based compound, a polyphosphazene based compound,polypropylene oxide, polymethyl metacrylate, polymetacrylonitrile, and apolyether based compound. The above high polymer may be copolymerizedwith another high polymer. From the viewpoints of chemical stability andion conductivity, there is preferably used a material produced bycopolymerization of polyvinylidene fluoride and polyhexafluoropropyleneat a copomerization ratio of less than 8 wt %.

The gel-like electrolyte contains the electrolyte salt, the matrixpolymer, and a swelling solvent as a plasticizer.

As the plasticizer used for forming the gel-like electrolyte from thehigh polymer solid electrolyte, there can be used nonaqueous solventssuch as ethylene carbonate, propylene carbonate, γ-butyrolactone,acetonitrile, diethyl ether, diethyl carbonate, dimethyl carbonate,1,2-dimethoxyethane, dimethyl sulfoxide, 1,3-dioxolane, methylsulfonate, 2-methyltetrahydrofuran, tetrahydrofuran, sulfolane,2,4-difluoroanisole, and vinylene carbonate. These nonaqueous solventscan be used singly or in combination.

At the terminal extraction port formed at the position of the positivecollector exposed portions 2 c butted to each other, the sealing member5 is disposed at a portion at which the negative electrode terminal 4 isin contact with the positive collector exposed portions 2 c. To be morespecific, the negative electrode terminal 4 is covered with the sealingmember 5 and is held between the positive collector exposed portions 2c, to prevent the negative electrode terminal 4 from beingshort-circuiting with the positive electrodes 2 due to burrs or the likeformed on the positive electrodes 2, and to improve the air-tightness atthe terminal extraction port. The material of the sealing member 5 isnot particularly limited insofar as it exhibits an adhesive propertyagainst the electrode terminal but is preferably selected frompolyolefin resins such as polyethylene, polypropylene, denaturedpolyethylene, denatured polypropylene, and copolymers thereof.

As described above, the pair of positive electrodes 2 seal the negativeelectrode 3 and the solid electrolyte layers 6 therein by joining thepositive collector exposed portions 2 c to each other with the positivecollectors 2 a directly outwardly. Accordingly, since the positiveelectrodes 2 serve as a container, it is not required to provide a newcontainer and to provide a new terminal for the positive electrodes 2serving as the container. As a result, it is possible to further thinthe solid electrolyte battery 1, to further reduce the weight thereof,and to further improve the energy density thereof.

The pair of positive electrodes 2 seal the negative electrode 3 and thesolid electrolyte layers 6 therein by directly joining the positivecollector exposed portions 2 c provided at the outer peripheral edgeportions of the positive electrodes 2 to each other not via a resin forheat seal. Since any resin for heat seal through which moisture maypermeate is not used, it is possible to prevent deterioration of thecharging/discharging cycle due to permeation of moisture. Further, thewidth of each of the positive collector exposed portions 2 c as thejoining margins can be made narrower than that of the related artsticking margin, it is possible to make smaller the areas of thepositive collector exposed portions 2 c not contributing to the batteryreaction, and hence to further improve the energy density of the solidelectrolyte battery 1.

The solid electrolyte battery 1 having the above-described configurationis produced as follows:

A positive electrode 2 is produced by forming a positive active materiallayer 2 b on one surface of a positive collector 2 a.

One surface of metal foil, for example, aluminum foil, which becomes thepositive collector 2 a, is uniformly coated with a positive mixcontaining a positive active material and a binder. In this case, theouter peripheral edge portion of the positive collector 2 a is notcoated with the positive mix, and remains as a positive collectorexposed portion 2 c. The positive mix is then dried, to form thepositive active material layer 2 b. The positive electrode 2 is thusproduced. As the binder of the positive mix, a known binder can be used,and further, known additives may be added to the positive mix. Thepositive active material layer 2 b can be also formed by using castcoating or sintering.

The positive collector exposed portion 2 c, which is the outerperipheral edge portion, not covered with the positive active materiallayer 2 b, of the positive collector 2 a, may be formed by forming thepositive active material layer 2 b over one surface of the positivecollector 2 a and removing a portion of the positive active materiallayer 2 b formed on the outer peripheral edge portion of the positiveelectrode 2, or forming the positive active material layer 2 b at apredetermined shape (excluding the outer peripheral edge portion) on onesurface of the positive collector 2 a by pattern coating or the like. Inthis way, according to this embodiment, the method of forming thepositive collector exposed portion 2 c is not particularly limited.

A negative electrode 3 is produced by forming a negative active materiallayer 3 b on one surface of a negative collector 3 a.

Both surfaces of metal foil, for example, copper foil, which becomes thenegative collector 3 a, are uniformly coated with a negative mixcontaining a negative active material and a binder, followed by dryingthe negative mix, to form the negative active material layer 3 b. Thenegative electrode 3 is thus produced. As the binder of the negativemix, a known binder can be used, and further, known additives may beadded to the negative mix. The negative active material layer 3 b can bealso formed by using cast coating or sintering.

The order of producing each of the positive electrode 2 and the negativeelectrode 3 is not particularly limited. For example, the electrode canbe produced by forming the active material layer on the collector, andthen cutting the collector into a specific shape corresponding to thatof the electrode, or cutting the collector into a shape corresponding tothat of the electrode, and then forming the active material layer on thecollector.

A solid electrolyte layer 6 is formed on each of the negative activematerial layers 3 b formed on both the surfaces of the negativeelectrode 3. For example, in the case of using a gel-like electrolyte asthe solid electrolyte layer 6, a plasticizer is first prepared bydissolving an electrolyte salt in a nonaqueous solvent. A matrix polymeris then added to the plasticizer, and is dissolved therein by agitation,to obtain a sol-like electrolytic solution. The negative active materiallayer 3 b is coated with a specific amount of the electrolytic solutionand is left at room temperature until the matrix polymer gels. In thisway. the solid electrolyte layer 6 made from the gel-like electrolyte isformed on the negative active material layer 3 b.

Similarly, a solid electrolyte layer 6 is formed on the positive activematerial layer 2 b formed on the one surface of the positive electrode2.

A negative electrode terminal 4 is connected to part of the negativecollector 3 a of the negative electrode 3. A sealing member 5 made froman insulating material is previously stuck on a portion, to be broughtinto contact with the exposed portions of the positive collectors 2 a,of the negative electrode terminal 4.

Next, as shown in FIG. 4, the negative electrode 3 is held between thepair of positive electrodes 2 in such a manner that the positive activematerial layers 2 b are opposed to the negative active material layers 3b via the solid electrolyte layers 6. To be more specific, the positiveelectrode 2 having the solid electrolyte layer 6 on its one surface, thenegative electrode 3 having the solid electrolyte layers 6 on its bothsurfaces, and the positive electrode 2 having the solid electrolytelayer 6 on its one surface are stacked to each other in such a mannerthat the solid electrolyte layers 6 are in contact with each other. Atthis time, the positive collector exposed portions 2 c provided at theouter peripheral edge portions of the positive electrodes 2 are alignedand overlapped to each other. The negative electrode terminal 4connected to the negative electrode 3 is held between the positivecollector exposed portions 2 c via the sealing member 5, and is led tothe outside of the solid electrolyte battery 1.

In the case of using an electrolyte being low in diaphragmcharacteristic as the solid electrolyte layer 6, to prevent physicalcontact between the negative electrode 3 and each of the positiveelectrodes 2, as shown in FIG. 5. a separator 7 may be disposed betweenthe negative electrode 3 and the positive electrode 2. The separator 7may be made from a porous polyolefin resin or nonwoven fabric cloth.

Finally, the negative electrode 3 is sealed in the pair of the positiveelectrodes 2 by directly joining the positive collector exposed portions2 c, which have been aligned and overlapped to each other, to eachother, to produce the solid electrolyte battery 1 shown in FIGS. 1, 2and 3.

Here, the positive collector exposed portions 2 c can be joined to eachother by electron beam welding, laser welding, ultrasonic welding,resistance welding, or pressure welding.

However, at the terminal extraction port for leading the negativeelectrode terminal 4 to the outside of the solid electrolyte battery 1,the positive collector exposed portions 2 c are not directly joined toeach other by the above method but is sealed by heat seal via thesealing member 5.

As described above, according to the production method of the presentinvention, the whole of the outer peripheral edge portions of thepositive electrodes 2 serving as the container, excluding the terminalextraction port for the negative electrode 3 put in the positiveelectrodes 2, are directly joined to each other without use of a resinfor heat seal. Accordingly, it is possible to prevent permeation ofmoisture in the solid electrolyte battery 1, and hence to positivelykeep the air-tightness of the battery 1.

Further, since the areas of the positive collector exposed portions 2 cas the joining margins, which do not contribute to the battery reaction,can be reduced, it is possible to improve the energy density of thebattery 1.

In the above-described embodiment, the positive electrodes are used asthe first electrodes serving as the container and the negative electrodeis used as the second electrode sealed in the first electrodes; however,the present invention is not limited thereto but the negative electrodesmay be used as the first electrodes and the positive electrode be usedas the second electrode.

FIG. 6 is a perspective view showing another embodiment of a solidelectrolyte battery of the present invention; FIG. 7 is a sectional viewtaken on line E-F of FIG. 6; and FIG. 8 is a sectional view taken online G-H of FIG. 6. A solid electrolyte battery 11 has a pair ofnegative electrodes 12 as first electrodes, a positive electrode 13 as asecond electrode sealed in the negative electrodes 12, a positiveelectrode terminal 14 physically, electrically connected to the positiveelectrode 13, a sealing member 15 disposed between the positiveelectrode terminal 14 and the negative electrodes 12, and a pair ofsolid electrolyte layers 16.

The negative electrode 12 has a negative collector 12 a and a negativeactive material layer 12 b formed on one surface of the negativecollector 12 a. The negative active material layer 12 b is not formed onthe one surface of an outer peripheral edge portion of the negativecollector 12 a. Such an exposed outer peripheral edge portion is takenas a negative collector exposed portion 12 c.

The positive electrode 13 has a positive collector 13 a, and positiveactive material layers 13 b formed on both surfaces of the positivecollector 13 a. At a terminal extraction port formed at a position ofthe outer peripheral edge portions, butted to each other, of thenegative electrodes 12, the positive electrode terminal 14 is coveredwith the sealing member 15 to be thus insulated from the negativeelectrodes 12, and is lead to the outside of the solid electrolytebattery 11.

As shown in FIGS. 7 and 8, the positive electrode 13 having the positiveactive material layers 13 b on both surfaces of the positive collector13 a is held between the pair of negative electrodes 12 in such a mannerthat the positive active material layers 13 b are opposed to thenegative active material layers 12 b with the pair of solid electrolytelayers 16 put therebetween, and the positive electrode 13 is sealed,together with the pair of the solid electrolyte layers 16, in thenegative electrodes 12 by joining the negative collector exposedportions 12 c, which are formed at the outer peripheral edge portions ofthe negative electrodes 12 and which function as joining margins, toeach other.

As described above, the pair of the negative electrodes 12 seal thepositive electrode 13 and the solid electrolyte layers 16 therein byjoining the negative collector exposed portions 12 c, which function asthe joining margins, to each other with the negative collectors 12 adirected outwardly. In this way, since the negative electrodes 13 serveas the container, it is not required to provide a new container and alsoto provide a new terminal for the negative electrodes 12 serving as thecontainer. Accordingly, it is possible to further thin the solidelectrolyte battery 11, to further reduce the weight thereof, and tofurther improve the energy density thereof.

The pair of negative electrodes 12 seal the positive electrode 13 andthe solid electrolyte layers 16 by directly joining the negativecollector exposed portions 12 c provided at the outer peripheral edgeportions of the negative electrodes 12 to each other not via a resin forheat seal. Since any resin for heat seal through which moisture maypermeate is not used, it is possible to prevent deterioration of thecharging/discharging cycle due to permeation of moisture. Further, sincethe width of each of the negative collector exposed portions 12 cfunctioning as the joining margins can be made narrower than that of therelated art sticking margin for heat seal, it is possible to reduce theareas of the negative collector exposed portions 12 c not contributingto the battery reaction, and hence to further improve the energy densityof the solid electrolyte battery 11.

In addition, the solid electrolyte battery 11 shown in FIGS. 6, 7 and 8in which the negative electrodes are used as the first electrodes andthe positive electrode is used as the second electrode has the samebasic configuration as that of the solid electrolyte battery 1 shown inFIG. 1, except that the positive electrodes and the negative electrodein the battery 1 are replaced with the negative electrodes and thepositive electrode in the battery 11, respectively. Accordingly, theoverlapped description of each component in the battery 11,corresponding to that in the battery 1, is omitted.

Each of the batteries 1 and 11 according to the above-describedembodiments is configured so that the pair of the first electrodesserving as the container seal the second electrode and the solidelectrolyte layers by joining the collector exposed portions to eachother with the collectors of the first electrodes directed outwardly;however, the present invention is not limited thereto. For example, thepresent invention may be applied to a configuration in which one firstelectrode serving as a container is used in place of the pair of thefirst electrodes described in each of the batteries 1 and 11. In thisconfiguration, the first electrode is folded into two so as to hold thesecond electrode therein, to thereby seal the second electrode togetherwith the solid electrolyte layers.

FIG. 9 is a perspective view of a further embodiment of a solidelectrolyte battery of the present invention, in which only one firstelectrode serving as a container is used; FIG. 10 is a sectional viewtaken on line I-J of FIG. 9; and FIG. 11 is a sectional view taken online K-L of FIG. 9. A solid electrolyte battery 21 includes a positiveelectrode 22 as a first electrode, a negative electrode 23 as a secondelectrode sealed in the positive electrode 22, a negative electrodeterminal 24 physically, electrically connected to the negative electrode23, a sealing member 25 disposed between the negative electrode terminal24 and the positive electrode 22, and solid electrolyte layers 26.

The positive electrode 22 has a positive active material layer 22 bformed on one surface of the positive collector 22 a. The positiveactive material layer 22 b is not formed on the one surface of the outerperipheral edge portion of the positive collector 22 a. Such an exposedouter peripheral edge portion is taken as a positive collector exposedportion 22 c. Since the positive electrode 22 is folded into two so asto seal the negative electrode 23 therein, the size of the positiveelectrode 22 is set to be substantially twice the size of the negativeelectrode 23 so that one of the folded pieces of the positive electrode22 becomes nearly equal to that of the negative electrode 23.

The negative electrode 23 has a negative collector 23 a, and negativeactive material layers 23 b formed on both surfaces of the negativecollector 23 a. At a terminal extraction port formed at a position ofthe outer peripheral edge portion of the positive electrode 22, thenegative electrode terminal 24 is covered with the sealing member 25 tobe thus insulated from the positive electrode 22, and is led to theoutside of the solid electrolyte battery 21.

As shown in FIGS. 10 and 11, by folding the positive electrode 22 intotwo, the negative electrode 23 having the negative active materiallayers 23 b on both the surfaces of the negative collector 23 a is heldin the folded positive electrode 22 in such a manner that the negativeactive material layers 23 b are opposed to the positive active materiallayer 22 b via the solid electrolyte layers 26. At the same time, byjoining the positive collector exposed portion 22 c formed at the outerperipheral edge portion of the positive electrode 22 to each other oneach of three sides S1, S2 and S3 of the positive electrode 22, thenegative electrode 23 is sealed, together with the solid electrolytelayers 26, in the positive electrode 22.

As described above, the positive electrode 22 seals the positive activematerial layer 22 b, the negative electrode 23, and the solidelectrolyte layers 26 by folding the positive electrode 22 into two withthe positive collector 22 a directed outwardly, and then joining thepositive collector exposed portion 22 c to each other. In this way,since the positive electrode 22 serves as the container, it is notrequired to provide a new container and also to provide a new terminalfor the positive electrode 22 serving as the container. As a result, itis possible to further thin the solid electrolyte battery 21, to furtherreduce the weight thereof, and to further improve the energy densitythereof.

The positive electrode 22 seals the negative electrode 23 and the solidelectrolyte layers 26 by directly joining the positive collector exposedportion 22 c provided at the outer peripheral edge portion of thepositive electrode 22 to each other not via a resin for heat seal. Sinceany resin for heat seal through which moisture may permeate is not used,it is possible to prevent deterioration of the charging/dischargingcycle due to permeation of moisture. Further, since the width of thepositive collector exposed portion 22 c functioning as the joiningmargin can be made narrower than that of the related art sticking marginfor heat seal, it is possible to reduce the areas of the positivecollector exposed portion 22 c not contributing to the battery reaction,and hence to further improve the energy density of the solid electrolytebattery 21.

In addition, the solid electrolyte battery 21 shown in FIGS. 9, 10 and11 has the same basic configuration as that of the solid electrolytebattery 1 shown in FIG. 1, except that in the battery 21, one positiveelectrode as the first electrode is folded into two so as to hold thenegative electrode and the solid electrolyte layers therein.Accordingly, the overlapped description of each component in the battery21, corresponding to that in the battery 1, is omitted.

As described above, the first electrode may be configured as either ofthe negative electrode and the positive electrode and the secondelectrode be configured as the other of the negative electrode and thepositive electrode; however, the first electrode serving as thecontainer is preferably configured as the negative electrode. The use ofthe negative electrode as the first electrode capable of ensuring alarger area is effective to suppress precipitation of lithium at thetime of charging of the battery.

In each of the above-described solid electrolyte batteries, thethickness thereof is preferably in a range of 2 mm or less, morepreferably, 1 mm or less. In general, for a thin type battery, since thecontainer has a certain thickness and a certain weight, the effect ofthe container exerted on the volume and weight of the entire batterybecomes larger as compared with a battery having a relatively largethickness, with a result that the loss in energy density per volume andenergy density per weight becomes significant by the presence of thecontainer. According to the present invention, however, since it is notrequired to additionally provide the container, the present inventioncan be applied to a thin type sheet-like solid electrolyte battery. As aresult, it is possible to fully achieve the effects of the presentinvention, that is, the thinning, lightweightness, and higher energydensity of the battery.

In the above-described embodiments, the metal foil constituting thecollector is taken as the outermost layer of the battery, and thereby itfunctions as a container; however, the present invention is not limitedthereto. For example, the other surface, on which the active materiallayer is not formed, of the collector may be provided with a cover layeras the outermost layer of the battery by coating the other surface ofthe collector with nylon or the like. The provision of the cover layeris effective to impart a strength to the collector formed of the metalfoil and thereby reduce the thickness of the collector, and hence tofurther thin the battery, to reduce the weight thereof, and to furtherimprove the energy density thereof.

The shape of the solid electrolyte battery of the present invention isnot limited to the above-described square shape but may be any shape.Further, the present invention is applicable to both a primary batteryand a secondary battery.

The present invention will be more clearly understood by way of thefollowing examples:

INVENTIVE EXAMPLE

A negative electrode was produced in the following manner.

A negative mix was prepared by mixing 90 parts by weight of a crushedpowder of graphite as a negative active material and 10 parts by weightof poly(vinylidene fluoride-co-hexafluoropropylene) as a binder. Thenegative mix was dispersed in N-methyl-2-pyrrolidone to be slurried.Both surfaces of copper foil having a thickness of 10 μm as a negativecollector was uniformly coated with the slurry of negative mix, and thenegative mix was dried and compressed onto the negative collector by aroll press, whereby negative active material layers were formed on boththe surfaces of the negative collector. The negative electrode was thusproduced.

A positive electrode was produced in the following manner.

To obtain a positive active material (LiCoO₂), lithium carbonate andcobalt carbonate were mixed at a mixing ratio of 0.5 mol:1 mol, and weresintered in air at 900° C. for 5 hr. A positive mix was prepared bymixing 90 parts by weight of LiCoO₂ as the positive active material thusobtained, 6 parts by weight of graphite as a conductive agent, and 4parts by weight of poly(vinylidene fluoride-co-hexafluoropropylene) as abinder. The positive mix was dispersed in N-methyl-2-pyrrolidone to beslurried. One surface, excluding an outer peripheral edge portion, ofaluminum foil having a thickness of 40 μm as a positive collector wasuniformly coated with the slurry of positive mix by a pattern-coatingmanner, and the positive mix was dried and compressed onto the positivecollector by a roll press, whereby a positive active material layer wasformed on the one surface, excluding the outer peripheral edge portion,of the positive collector. The positive electrode was thus produced.

A gel-like electrolyte layer was produced in the following manner.

Each of the negative active material layers formed on both the surfacesof the negative collector and the positive active material layer formedon the one surface of the positive collector was uniformly coated with asolution, which was obtained by mixing and dissolving 30 parts by weightof a plasticizer containing 42.5 parts by weight of ethylene carbonate,42.5 parts by weight of propylene carbonate, and 15 parts by weight ofLiPF₆, 10 parts by weight of poly(vinylidenefluoride-co-hexafluoropropylene), and 60 parts by weight of dimethylcarbonate, to be impregnated therewith, and were left at roomtemperature for 8 hr to remove dimethyl carbonate by evaporation. Thegel-like electrolyte layers were thus produced.

The negative electrode having the solid electrolyte layers on both thesurfaces thereof was, as shown in FIG. 5, held and pressed between thepair of positive electrodes each having the solid electrolyte layer onthe one surface thereof.

Finally, positive collector exposed portions formed at the outerperipheral edge portions of the positive electrodes, excluding anegative terminal extraction port, were directly joined to each other byelectron beam welding, to thus produce a lithium ion secondary batteryhaving an A5 sheet shape (140 mm×196 mm) and a thickness of 560 μm.Additionally, at the negative terminal extraction port, an aciddenatured CPP film having a width of 8 mm and a thickness of 40 μm waspreviously stuck on the negative terminal. The negative extraction portwas sealed at 180° C. under a reduced pressure by using a heat sealer.

Comparative Example

A positive mix was prepared in the same manner as that in InventiveExample. One surface of aluminum foil having a thickness of 20 μm wasuniformly coated with the positive mix. The positive mix was dried andcompressed onto the aluminum foil by a roll press, to form a positiveactive material layer on the one surface of the aluminum foil. Apositive electrode was thus produced. Subsequently, a negative electrodewas produced in the same manner as that in Inventive Example.

Like Inventive Example, a gel-like electrolyte layer was formed on eachof the negative active material layers formed on both surfaces of thenegative collector and the positive active material layer formed on onesurface of the positive collector.

The positive electrode having the gel-like electrolyte layer, thenegative electrode having the gel-like electrolyte layers, and thepositive electrode having the gel-like electrolyte layer were overlappedto each other with the gel-like electrolyte layers opposed to eachother, and were brought into press-contact with each other, to produce abattery element.

The battery element thus produced was inserted in an aluminum laminatefilm composed of a cast polypropylene layer (30 μm), aluminum foil (40μm), and a nylon layer (15 μm), and the outer peripheral edge portion ofthe aluminum laminate film was sealed at 180° C. under a reducedpressure by using a heat sealer, to produce a sheet-like lithium ionsecondary battery having a size of 140 mm×200 mm and a thickness of 690μm.

With respect to the batteries in Inventive Example and ComparativeExample, an energy density at the beginning of the charging/dischargingcycle and a discharge capacity retention ratio after 500 cycles weremeasured. The results are shown in Table 1.

TABLE 1 Energy Energy Discharge density per density per capacity weightvolume retention ratio (Wh/kg) (Wh/L) (%) Inventive 148 310 81 ExampleComparative 131 290 39 Example

As is apparent from Table 1, the battery in Inventive Example issuperior to the battery in Comparative Example in energy density perweight, energy density per volume, and discharge capacity retentionratio. As a result, it is found that the configuration in which thepositive electrode serves as the container is effective to improve theenergy density of the battery, and that the configuration in which thepositive collector exposed portions are directly joined to each other iseffective to positively keep the air-tightness and hence to preventdeterioration of the charging/discharging cycle due to permeation ofmoisture.

As described above, according to the solid electrolyte battery of thepresent invention, since the first electrodes serve as the container, itis not required to provide a new terminal for the first electrodes andto provide a new container, and hence to further thin the battery and tofurther reduce the weight thereof. Since the battery can be mounted onan electronic apparatus without any limitation to the position of theterminal of the first electrodes, it is possible to thin the electronicapparatus and to reduce the weight thereof. Further, since the solidelectrolyte battery is sealed by directly joining the collector exposedportions provided at the outer peripheral edge portions of the firstelectrodes to each other not via a resin for heat seal, it is possibleto ensure a significantly desirable air-tightness, and to significantlyreduce the areas of the collector exposed portions of the firstelectrodes. Accordingly, it is possible to realize the thinning,iightweightness, and higher energy density of the solid electrolytebattery, and to enhance the charging/discharging cycle characteristicthereof.

According to the method of producing a solid electrolyte battery of thepresent invention, since the battery is sealed by directly joining thecollector exposed portions of the first electrodes to each other not viaa resin for heat seal, it is possible to realize thinning andlightweightness of the battery, and to ensure a significantly desirableair-tightness thereof. Accordingly, it is possible to provide a thin,lightweight solid electrolyte battery having a higher energy density andan excellent charging/discharging cycle characteristic.

While the preferred embodiments of the present invention have beendescribed using the specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the followingclaims.

What is claimed is:
 1. A solid electrolyte battery comprising: a firstelectrode including a first collector, and a first active material layerformed on one surface of said first collector with an outer peripheraledge portion of said first collector remaining as a collector exposedportion; a second electrode including a second collector and secondactive material layers formed on both surfaces of said second collector;and a solid electrolyte interposed between said first electrode and saidsecond electrode; wherein said second electrode is held in said firstelectrode in such a manner that said first active material layer isopposed to each of said second active material layers via said solidelectrolyte, and is sealed in said first electrode by joining saidcollector exposed portion of said first electrode to each other.
 2. Asolid electrolyte battery according to claim 1, comprising a pair offirst electrodes, and said second electrode is held between said firstelectrodes.
 3. A solid electrolyte battery according to claim 1, furthercomprising an electrode terminal connected to said second electrode,wherein said electrode terminal is led to the outside while being heldin the joined portion of said collector exposed portion of said firstelectrode.
 4. A solid electrolyte battery according to claim 3, furthercomprising a sealing member having electric insulation, which isdisposed between said electrode terminal and said first electrode.
 5. Asolid electrolyte battery according to claim 1, wherein said solidelectrolyte is made to gel by using a plasticizer.
 6. A solidelectrolyte battery according to claim 1, wherein said battery is formedinto a sheet having a thickness of 2 mm or less.
 7. A solid electrolytebattery according to claim 1, further comprising a separator disposedbetween said first electrode and said second electrode.
 8. A solidelectrolyte battery according to claim 1, wherein said first electrodeis a negative electrode, and said second electrode is a positiveelectrode.
 9. A solid electrolyte battery according to claim 8, whereinsaid negative electrode contains lithium, a lithium alloy, or a materialinto or from which lithium can be doped or released.
 10. A solidelectrolyte battery according to claim 8, wherein said positiveelectrode contains a composite oxide of lithium and a transition metal.11. A solid electrolyte battery according to claim 1, wherein said firstelectrode is a positive electrode, and said second electrode is anegative electrode.
 12. A solid electrolyte battery according to claim11, wherein said negative electrode contains lithium, a lithium alloy,or a material into or from which lithium can be doped or released.
 13. Asolid electrolyte battery according to claim 1l, wherein said positiveelectrode contains a composite oxide of lithium and a transition metal.14. A method of producing a solid electrolyte battery, comprising thesteps of: forming a first active material layer on one surface of afirst collector with an outer peripheral edge portion of the firstcollector remaining as a collector exposed portion, to produce a firstelectrode; forming second active material layers on both surfaces of asecond collector, to produce a second electrode; holding the secondelectrode in the first electrode in such a manner that the first activematerial layer is opposed to each of the second active material layersvia a solid electrolyte; and joining the collector exposed portion ofthe first electrode, in which the second electrode has been held in saidholding step, to each other, to seal the second electrode in the firstelectrode.
 15. A method of producing a solid electrolyte batteryaccording to claim 14, wherein in said sealing step, the collectorexposed portion of said first electrode is joined to each other byeither of electron beam welding, laser welding, ultrasonic welding,resistance welding, and pressure welding.
 16. A method of producing asolid electrolyte battery according to claim 14, wherein a pair of firstelectrodes are produced in said first producing step, and in saidholding step, the second electrode is held between the pair of firstelectrodes.
 17. A method of producing a solid electrolyte batteryaccording to claim 14, wherein in said holding step, an electrodeterminal is connected to the second electrode, and the electrodeterminal is led to the outside while being held in the joined portion ofthe collector exposed portion of the first electrode.
 18. A method ofproducing a solid electrolyte battery according to claim 17, wherein insaid sealing step, a sealing member having electric insulation isdisposed between the electrode terminal and the first electrode, and aportion, at which the sealing member is disposed, of the collectorexposed portion of the first electrode is joined to each other by heatseal via the sealing member.
 19. A method of producing a solidelectrolyte battery according to claim 14, wherein the solid electrolyteis made to gel by using a plasticizer.
 20. A method of producing a solidelectrolyte battery according to claim 14, wherein the battery is formedinto a sheet having a thickness of 2 mm or less.
 21. A method ofproducing a solid electrolyte battery according to claim 14, furthercomprising the step of disposing a separator between the first electrodeand the second electrode.
 22. A method of producing a solid electrolytebattery according to claim 14, wherein the first electrode is a negativeelectrode, and the second electrode is a positive electrode.
 23. Amethod of producing a solid electrolyte battery according to claim 22,wherein the negative electrode contains lithium, a lithium alloy, or amaterial into or from which lithium can be doped or released.
 24. Amethod of producing a solid electrolyte battery according to claim 22,wherein the positive electrode contains a composite oxide of lithium anda transition metal.
 25. A method of producing a solid electrolytebattery according to claim 14, wherein the first electrode is a positiveelectrode, and the second electrode is a negative electrode.
 26. Amethod of producing a solid electrolyte battery according to claim 25,wherein the negative electrode contains lithium, a lithium alloy, or amaterial into or from which lithium can be doped or released.
 27. Amethod of producing a solid eletrolyte battery according to claim 25,wherein producing a solid electrolyte contains a composite oxide oflithium and transition metal.